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Daniel Brown, Rick Knabb, Mike Brennan & Mark DeMaria. Tropical Cyclone Wind Speed Probabilities: Recent Developments and Future Plans. MC Probability Example Hurricane Ike – 7 Sept 2008 12 UTC. 1000 Track Realizations. 64 kt 0-120 h Cumulative Probabilities. - PowerPoint PPT Presentation
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Daniel Brown, Rick Knabb, Mike Brennan & Mark DeMaria
Daniel Brown, Rick Knabb, Mike Brennan & Mark DeMaria
Tropical Cyclone Wind SpeedProbabilities: Recent Developments and
Future Plans
Tropical Cyclone Wind SpeedProbabilities: Recent Developments and
Future Plans
1000 Track Realizations
MC Probability ExampleHurricane Ike – 7 Sept 2008 12 UTC
64 kt 0-120 h Cumulative Probabilities
JHT Project Tasks(from DeMaria and Kidder)
Improved Monte Carlo wind probabilities using situationally-dependent track error distributions (2007-2009)
-Track error depends on Goerss Predicted Consensus Error (GPCE)
Decrease time step to one hour (2009-11)-Reduces noise for fast moving storms, also needed for landfall applications
Landfall timing and intensity distributions (2009-11)
-Intensity probability table began using Monte Carlo technique in 2008-Accounts for land but does not provide assessment of landfall intensity probabilities as probabilities are valid only at a point in time-Develop tools to convey wind timing uncertainty
-inclusion in HURREVAC?
Line integral probabilities (2009-11)-Could be used to estimate the probability that any portion of the warning area would receive hurricane force winds
Hurricane Watch/Warning Guidance (2009-11)
Goerss Predicted Consensus Error (GPCE)
Predicts error of TVCN track forecast• Consensus of GFS, UKMET, NOGAPS, GFDL, HWRF, GFDN, ECMWF
GPCE Input• Spread of TVCN member track forecasts• Initial latitude• Initial and forecasted intensity
Explains 15-50% of TCVN track error variance
GPCE estimates radius that contains ~70% of TCVN verifying positions at each forecast time
Task 1: Forecast Dependent Track Errors
Use GPCE input as a measure of track uncertainty
Divide NHC track errors into three bins based on GPCE values• Low, Medium and High
For real time runs, use probability distribution for the appropriate real time GPCE value tercile
• Different forecast times can use different distributions
Relies on relationship between NHC track errors and GPCE value
Probabilities tighten (spread) when GPCE values are small (large)
72 hr Atlantic NHC Along Track Error Distributions Stratified by GPCE
0
5
10
15
20
25
30
35
40
-600 -400 -200 0 200 400 600 800
Along Track Error (nmi)
Fre
qu
en
cy
(%
)
Lower GPCE Tercile
Upper GPCE Tercile
DeMaria et al. 2009 (accepted to Wea. Forecasting)
Evaluation Procedure
Near real time parallel runs began during second half of 2008 hurricane season and continued through 2009
Qualitative Evaluation: 34, 50, and 64 kt probabilities posted to web page for evaluation
-Operational, GPCE, and difference plots
Quantitative Evaluation: Calculate probabilistic forecast metrics from output on NHC breakpoints
-Performed by DeMaria et al. for 2008 cases.
-2009 verification for Atlantic and east, central, west Pac will be included in final report 12/4/09
Current Operational VersionCurrent Operational Version
Experimental VersionExperimental Version
34 kt 0-120 h cumulative probability difference field (GPCE-Operational)
GPCE values in “low” tercile through 72 h “medium” tercile at 96 h
Qualitative Evaluation Tropical-Storm-Force Wind Probabilities
Ida- Advisory #14
Current Operational VersionCurrent Operational Version
Experimental VersionExperimental Version
34 kt 0-120 h cumulative probability difference field (GPCE-Operational)
All GPCE values in “low” tercile
Qualitative Evaluation Tropical-Storm-Force Wind Probabilities
Bill- Advisory #18
64 kt 0-120 h cumulative probability difference field (GPCE-Operational)
All GPCE values in “low” tercileExperimental VersionExperimental Version
Current Operational VersionCurrent Operational Version
Experimental VersionExperimental Version
Qualitative Evaluation Hurricane-Force Wind Probabilities
Bill- Advisory #18
2008 Quantitative EvaluationCalculate probabilities at NHC breakpoints
-Operational and GPCE versions -34, 50, and 64 kt -12-hr cumulative and incremental to 120 h
-169 forecasts X 257 breakpoints = 43,433 data points at each forecast time
Two evaluation metrics -Brier Score -Optimal Threat Score
Brier Score Improvements2008 GPCE MC Model Test
0
1
2
3
4
5
6
7
8
9
10
12 24 36 48 60 72 84 96 108 120
Forecast Period
Bri
er S
core
Imp
rove
men
t (%
)
64 kt Cumulative
50 kt Cumulative
34 kt Cumulative
0
1
2
3
4
5
6
7
8
9
10
12 24 36 48 60 72 84 96 108 120
Forecast PeriodB
rier
Sco
re Im
pro
vem
ent
(%)
64 kt Incremental
50 kt Incremental
34 kt Incremental
Cumulative Incremental
Threat Score Improvements2008 GPCE MC Model Test
-6
-4
-2
0
2
4
6
8
10
12
12 24 36 48 60 72 84 96 108 120
Forecast Period (hr)
TS
Ove
rlap
Are
a In
crea
se (
%)
64 kt Incremental
50 kt Incremental
34 kt Incremental
-6
-4
-2
0
2
4
6
8
10
12
12 24 36 48 60 72 84 96 108 120
Forecast Period (hr)
TS O
verl
ap A
rea
Incr
ease
(%
)
64 kt Cumulative
50 kt Cumulative
34 kt Cumulative
Cumulative Incremental
Intensity Probability Table• Provides chances that the
intensity will fall within certain categories
• Land effects included in calculation
• For storms near land the probabilities tend to be more evenly spread among the various categories
• Provides intensity probabilities for a specific time, not location Cannot be used for to determine landfall intensity
• Decision makers are looking for landfall intensity probabilities -What is the chance the storm will be category 3 at landfall?
Dean 2007 Isabel 2003
<1% <1% <1% <1% 1% 3% 17%
<1% <1% <1% <1% 1% 3% 14%
<1% <1% 1% 1% 4% 22% 21%
99% 99% 99% 99% 95% 72% 47%
<1% 2% 5% 5% 8% 29% 17%
3% 7% 9% 10% 14% 22% 13%
58% 43% 33% 36% 28% 16% 11%
38% 44% 44% 40% 33% 5% 5%
1% 4% 8% 10% 12% 1% 1%
Maximum Wind Speed (Intensity) Probability TableFrom NHC Advisory 185 PM EDT Aug 17, 2007
<1% <1% <1% <1% <1% <1% 1%
<1% <1% <1% <1% <1% 1% 1%
<1% <1% <1% 2% 3% 7% 10%
100% 100% 100% 98% 97% 92% 89%
<1% 1% 3% 9% 13% 18% 22%
1% 3% 10% 17% 19% 21% 20%
29% 25% 40% 40% 34% 31% 26%
67% 63% 41% 27% 24% 19% 17%
3% 9% 6% 5% 6% 4% 3%
Maximum Wind Speed (Intensity) Probability TableFrom NHC Advisory 155 PM EDT Sep 9, 2003
NHC Forecast 140 145 140 135 135 125 125NHC Forecast 130 140 145 150 150 115 120
More interaction with landMore tracks remaining
over waterless probability of hurricane higher probability
of hurricane
Verifying IntensityVerifying Intensity
KatrinaAdvisory #14
<1% <1% <1% <1% 8% 46% 58%
<1% <1% <1% <1% 13% 26% 20%
1% 3% 4% 5% 20% 13% 6%
99% 97% 96% 94% 58% 15% 17%
26% 21% 19% 18% 14% 3% 2%
60% 47% 34% 26% 12% 2% 4%
13% 25% 34% 34% 19% 5% 5%
1% 3% 7% 14% 12% 4% 4%
<1% <1% 1% 2% 3% 1% 1%
Maximum Wind Speed (Intensity) Probability TableFrom NHC Advisory 145 PM EDT Aug 26, 2005
Official NHC Intensity Forecast72 hour forecast- 135 mph (cat. 4)
NHC Forecast 105 110 115 120 135 40 30
Katrina Landfall Intensity 130 mph (cat. 3)
18
t=72 h Many tracks already
inland at 72 h
VerifyingIntensitycat. 1
Landfall Intensity Probability Example
• Prototype GUI allows user to select breakpoints for landfall probability applications-Includes landfall timing, intensity distributions, line integral probs, watch/warning guidance
• Could be transitioned to ATCF
Line Integral Probabilities
Hurricane Ike 12 Sept 2008 00 UTC
Maximum 0-120 hr cumulative 64 kt wind prob = 53%
98.3% of realizations cross the coast between Port Aransas and Morgan City
Line integral probability of 64 kt winds anywhere between Port Aransas and Morgan City = 75%
o Port Aransas
o Morgan City
NHC Hurricane Warnings Objective Scheme Hurr Warnings
Future: Watch/Warning Guidancefrom Shumacher et al.
First Guess (Prelim w/ Ivan) : pup = 10.0%, pdown = 2.0%
Best fit: pup = 8.0%, pdown = 0.0%
Summary• Continue evaluation of GPCE version of wind probabilities
-Decision on implementation (2007-09 JHT project) by spring 2010
• Landfall intensity probabilities -Specialists expected to have the capability to examine landfall
intensity probabilities during 2010 season -Possible inclusion of landfall probabilities in tropical cyclone
discussion
• Line integral probabilities -May have the capability to examine these in 2010
• Hurricane watch/warning guidance-Still a couple of years away
-Changes to watch/warning lead times could impact development -Hoped that objective watch/warning guidance could be used for
collaborative TC watch/warning approach